In the cracking of feedstocks to produce alkenes the resulting product is typically a mixture of various alkenes, such as ethylene and propylene and various alkanes or paraffins such as ethane, propane, and higher alkanes. With close boiling products such as ethylene and ethane and propylene and propane it is necessary to separate the products using distillation methods. The distillation may be carried out at very low temperatures or may be carried out using higher pressures and corresponding higher temperatures.
It is known to separate olefins from paraffins by forming complexes with metals such as silver or copper. The resulting copper or silver complex is preferentially soluble in a liquid not miscible or soluble in the paraffin, such as water. The streams are separated and then the olefin is released from the complex typically by a temperature or pressure change. The regenerated metal compound is then capable of being reused to complex more olefin. In some cases the metal compound is adsorbed or complexed on the surface of an ion exchange resin or in a membrane separation film and the olefin is separated from the alkane. Representatives of such art include Canadian patent 1,096,779 issued Mar. 3, 1981 to Deutsche Texaco A.G.; U.S. Pat. No. 3,979,280 issued Sep. 7, 1976 and assigned to Deutsche Texaco A.G.; U.S. Pat. No. 4,328,382 issued May 4, 1982 assigned to Erdoelchemie G.m.b.H.; and U.S. Pat. No. 3,441,377, issued Apr. 29, 1969 to Esso Research and Engineering Co.
Most recent in this line of technology is U.S. Pat. No. 6,339,182 B1 issued Jan. 15, 2002 to Munson et al., assigned to Chevron U.S.A. Inc. This patent teaches the absorption of alkenes by metal salts, typically silver or copper salts in ionic liquids. The alkenes are typically initially present as an admixture with paraffins. The alkenes are regenerated by separation from the metal complex by temperature or pressure change or application of an entrainment gas such as an inert gas.
The present invention is distinct over the above art as it does not require the presence of a metal complex. Applicants have discovered that olefins are preferentially soluble in some ionic liquids without the presence a metal (e.g. silver or copper) salt.
The present invention seeks to provide a simple process for the separation of alkenes from other hydrocarbons, particularly alkanes.